webpack/lib/FlagDependencyUsagePlugin.js

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
"use strict";

const addToSet = (a, b) => {
	for(const item of b) {
		if(!a.includes(item))
			a.push(item);
	}
	return a;
};

const isSubset = (biggerSet, subset) => {
	if(biggerSet === true) return true;
	if(subset === true) return false;
	return subset.every(item => biggerSet.indexOf(item) >= 0);
};

class FlagDependencyUsagePlugin {
	apply(compiler) {
		compiler.hooks.compilation.tap("FlagDependencyUsagePlugin", (compilation) => {
			compilation.hooks.optimizeModulesAdvanced.tap("FlagDependencyUsagePlugin", (modules) => {

				const processModule = (module, usedExports) => {
					module.used = true;
					if(module.usedExports === true)
						return;
					else if(usedExports === true)
						module.usedExports = true;
					else if(Array.isArray(usedExports)) {
						const old = module.usedExports ? module.usedExports.length : -1;
						module.usedExports = addToSet(module.usedExports || [], usedExports);
						if(module.usedExports.length === old)
							return;
					} else if(Array.isArray(module.usedExports))
						return;
					else
						module.usedExports = false;

					// for a module without side effects we stop tracking usage here when no export is used
					// This module won't be evaluated in this case
					if(module.factoryMeta.sideEffectFree) {
						if(module.usedExports === false) return;
						if(Array.isArray(module.usedExports) && module.usedExports.length === 0) return;
					}

					queue.push([module, module.usedExports]);
				};

				const processDependenciesBlock = (depBlock, usedExports) => {
					for(const dep of depBlock.dependencies) {
						processDependency(dep);
					}
					for(const variable of depBlock.variables) {
						for(const dep of variable.dependencies) {
							processDependency(dep);
						}
					}
					for(const block of depBlock.blocks) {
						queue.push([block, usedExports]);
					}
				};

				const processDependency = dep => {
					const reference = dep.getReference && dep.getReference();
					if(!reference) return;
					const module = reference.module;
					const importedNames = reference.importedNames;
					const oldUsed = module.used;
					const oldUsedExports = module.usedExports;
					if(!oldUsed || (importedNames && (!oldUsedExports || !isSubset(oldUsedExports, importedNames)))) {
						processModule(module, importedNames);
					}
				};

				for(const module of modules) {
					module.used = false;
				}

				const queue = [];
				for(const chunk of compilation.chunks) {
					if(chunk.entryModule) {
						processModule(chunk.entryModule, true);
					}
				}

				while(queue.length) {
					const queueItem = queue.pop();
					processDependenciesBlock(queueItem[0], queueItem[1]);
				}
			});
		});
	}
}
module.exports = FlagDependencyUsagePlugin;